In general, a large-sized transporter vehicle called a dump truck has a liftable vessel (loading platform) on a frame of a vehicle body, and transports crushed stones or the like in a state of a heavy baggage being loaded in a large quantity on the vessel.
Therefore, each travel drive device for driving drive wheels of the dump truck for traveling is provided with an axle housing mounted in a non-rotating state on a vehicle body and having a tip end side opened to form a cylindrical spindle, a rotational shaft provided to axially extend in the spindle of the axle housing and driven and rotated by a drive source, a wheel mounting cylinder which is rotatably mounted on an outer peripheral side of the spindle through a wheel support bearings and to which wheels are mounted, and a reduction gear mechanism provided between the wheel mounting cylinder and the spindle to decelerate rotation of the rotational shaft, which is transmitted to the wheel mounting cylinder (Patent Documents 1 and 2).
The reduction gear mechanism is constituted by a multi-stage planetary gear reduction mechanism comprising a sun gear, a plurality of planetary gears meshing with the sun gear and a ring-shaped internal gear, and a carrier rotatably supporting the respective planetary gears through support pins. The carrier forming a part of a final-stage planetary gear reduction mechanism is configured to be mounted in a non-rotating state on an open end side of the spindle.